Alloy for electrical contacts



Patented Oct. 28, 1930 UNITED STATES PATENT OFFICE EDWIN I. KINGSBURY, OF RUTHERFORD, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK No Drawing.

This invention relates to alloys for use as a contact metal for electric circuit makers and breakers.

The object of the invention is to improve the operation of electrical contacts.

Considerable difficulty has been experienced in the use of electrical contact materials for circuit making and breaking contacts of relays, switches and other apparatus. In the case of the noble metals, which are frequently used as contact materials, the continuous sparking produced by making and breaking of the contacts results in the contact surface becoming roughened or pitted and the apparent building up of fine needle points on one or the other or both of the contact surfaces thus varying the spacing between contacts and ultimately in many cases causing short circuits across the contacts. On the other hand, when base metals are employed as contact materials a film of oxide of the metal is readily formed on the contact surface which may result either in false operation or an increase in contact resistance or both. Telephone and telegraph repeating relays are ordinarily operated by currents so small that the resulting small contact pressures give rise to considerable heating. Development work in connection with such relays has led to this invention, which, however, is applicable in other types of circuit making and breaking devices.

This invention provides a relatively inexpensive alloy the main constituents of which are palladium and a semi-noble metal of the tungsten group, such as tungsten and molybdenum, which. possesses the strength, hardness, resiliency and homogeneity of composition which is necessary in contact materials. The constituents of this alloy may be so proportioned that the contact resistance is not unsatisfactorily high and at the same time the contact surfaces remain substantially unchanged in character and continue to function uniformly over a relatively great period. It appears that the improved result is obtained by virtue of the slight oxidizing property of the alloy. It seems probable that the transfer of material from one contact to the other and the conse- Application filed March 2, 1926. Serial No. 91,818.

quent building up of needle points is prevented or at least very greatly reduced by the oxidizing of the material at the contact points, this oxidizing being just sufiicient for this purpose. The pitting of the contacts is likewise greatly diminished, which is perhaps due in part at least to a reduction in the amount of heating at the point of contact.

The homogeneity of composition referred to above is essential in contact alloys, since the actual contact area at any one time is extremely small and it is impossible to obtain consistent results where appreciable nonuniformity exists. In the case of many alloys heretofore proposed, even a thorough mechanical working does not produce a homogeneity of structure suflicient for contact purposes.

The proportions of palladium and tungsten or molybdenum which may be employed in forming the contact alloys of the invention may be considerably varied, depending upon the condition under which the contact is to be used, changes in such proportions, of course, varying the contact resistance, the tendency to oxidize and the tendency towards transfer of material between the contacts of the particular alloy employed. It has been found by test that binary alloys containing palladium and tungsten in widely varying proportions show considerably less disintegration than either constituent used alone. The same results were obtained with alloys of palladium and molybdenum.

The composition which has been found preferable consists of palladium and tungsten in which the palladium is in excess atomically, that is, a binary alloy of palladium and tungsten in which the palladium content is greater than 36.7 percent by weight of the whole. A specific alloy which is very satis' factory in fulfilling the requirements enumerated above consists of 7 0 percent palladium and 30 percent tungsten by weight; but these proportions may be varied, as pointed out above.

If desired, the alloy may include a small amount of nickel as a third constitutent, the addition of which will tend to increase the ductility of the alloy, and will also serve to increase the effective solubility limit of tungsten in palladium.

Furthermore, ordinary commercial palladium often contains traces of other metals 5 such as gold, silver and platinum, and the presence of small quantities of such metals in the alloy is not to be construed as a departure from the scope and spirit of the invention.

What is claimed is:

1. A contact element composed of an alloy comprising palladium and a metal of the tungsten group as the essential elements thereof.

2. A contact element composed of an alloy containing palladium and a metal of the tungsten group as the essential elements thereof, the palladium being in excess atomicall 3. A contact element composed of a binary alloy comprising palladium and a metal of the tungsten group, in which the palladium is in excess atomically.

4. A contact element composed of an alloy comprising palladium and tungsten as the essential elements thereof.

5. A contact element-composed of an alloy containing palladium and tungsten as the essential elements thereof, the palladium being in excess atomically.

6. A contact element composed of a binary alloy comprising palladium and tungsten, in which the palladium is in excess atomically.

7 A contact element composed of an alloy containing palladium and tungsten as the essential elements thereof, in which the proportion of palladium is substantially 70% by weight of the whole.

8. A contact element composed of a binary alloy comprising substantially 70% by weight of palladium and 30% by weight of tungsten.

9. A contact element composed of an alloy containing palladium, tungsten and a third metal which has the property of increasing the ductility of the alloy and the effective solubility limit of tungsten in palladium.

10. A contact element composed of an alloy containing palladium, tungsten and nickel as the essential elements thereof.

In witness whereof, I hereunto subscribe my name this 25th day of February, A. D.

EDWIN F. KIN GSBURY. 

